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Okay, so here's the deal. For a while now I've been working with the OfflineList dat files from Advanscene, and for the love of me, I can't figure out what the "im1CRC" and "im2CRC" are CRC's of. Also, it would help if someone could help me identify ROMs quicker - instead of calculating the entire rom's CRC32, to calculate just a part - in a way that would work on trimmed roms too.

im1CRC and im2CRC are the CRC values for the box images, screen caps, etc.

EDIT: I can't see how scanning part of a ROM would work. Assuming you are talking about scaning for a certain file within the ROM you could end up getting a bad dump, where that file is the same as on a proper dump. The all over CRC is easier to calculate, but this would exclude trimmed ROMs because each time you trim it you would get a different CRC.

im1CRC and im2CRC are the CRC values for the box images, screen caps, etc.

EDIT: I can't see how scanning part of a ROM would work. Assuming you are talking about scaning for a certain file within the ROM you could end up getting a bad dump, where that file is the same as on a proper dump. The all over CRC is easier to calculate, but this would exclude trimmed ROMs because each time you trim it you would get a different CRC.

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Well the part of the rom I was thinking of scanning was the header. But, yeah that's exactly what I'm thinking. However when you're scanning 1000 files or even 200, Scanning each file can take a long time. That's why I don't get how OfflineList, Rominator and all those other rom managers can just scan a directory of 300 files and come up with the results in like 5 seconds.

Are there better ways of identifying roms with the information given in OfflineList's dat file? Or maybe there's another dat file I can use?